Electric heaters

ABSTRACT

A heater for use in a highly corrosive environment such as, for example, for heating pickling solutions, plating baths and the like, comprising an imperious graphite sheath, an electric heating element within the lower end of the sheath, granular refractory material within the sheath, an epoxy cement topping the refractory material and encapsulating a grounding plate which is in electrical engagement with the interior wall of the sheath, the entire heater being resistive to corrosive action of the heated solution or the fumes therefrom, and including a member to permit air to enter or exit from the sheath.

[ 51 May 23, 1972 1 ELECTRIC HEATERS [72] Inventor:

2,858,403 10/1958 Butler, Jr. 1,459,307 6/1923 Laise et al.... 2,754,407 7/1956 Steven J. Caroleo, Corapolis, Pa.

[73] Assignee: Emerson Electric Company, St. Louis, Mo.

[22] Filed: Jan. 8, 1971 Primary Examiner-C. L. Albritton Attomey-Michael Williams [21 A I. No.:

1 PP ABSTRACT A heater for use in a highly corrosive environment such as, for

example, for heating pickling solutions, plating baths and the M r i 3 65 3. M36 2/132 8 r t a 3 0 52 8 w 32 m n s ms,2 3 1 6 B "3 9 1 2 m WJZ u I u 8 u 0 I m T 6 u 3 u N 5 n u n 9 .l a taz QM C M U .m 1 I 2 8 5 55 I. [It

comprising an imperious graphite sheath, an electric heating element within the lower end of the sheath, granular refractory material within the sheath, an epoxy cement v topping the refractory material and encapsulating a grounding plate which is in electrical engagement with the interior wall of the sheath, the entire heater being resistive to corrosive action of the heated solution or the fumes therefrom, and including a member to permit air to enter or exit from the sheath.

UNITED STATES PATENTS Rapsis........a......................219/336 X 10 Claims, 5 Drawing figures Patented May 23, 1972 22 2a hehl sag 2mm INVENTOR. 7 STEVEN J. CAROLEO A TTORNE) ELECTRIC HEATERS BACKGROUND AND SUMMARY In the heating of highly corrosive solutions, such as hydrofluoric pickling solutions, copper fluoborate plating baths, and solutions containing hydrofluoric and concentrated phosphoric acids, great care is required in the design of the heater, not only to protect if from corrosive action from the solution itself but also from the fumes arising therefrom.

Heaters having impervious graphite sheaths have been produced prior to this invention and have enjoyed a measure of success. However, insofar as l am aware, no heater of prior art has the desirable constructional features detailed in the following description, including features of safety and efficiency.

Accordingly, it is a principal object of my invention to provide a new and improved heater of the character described.

DESCRIPTION OF THE DRAWING In the drawing accompanying this description and forming a part of this specification, there is shown, for purpose of illustration, an embodiment which my invention may assume, and in this drawing:

FIG. 1 is a longitudinal section of a heater, illustrating a preferred embodiment of my invention,

FIG. 2 is a top plan of the heater,

FIG. 3 is an enlarged sectional view corresponding to the line 3-3 of FIG. 1, and

FIGS. 4 and 5 are perspective views of details.

DESCRIPTION OF PREFERRED EMBODIMENT Referring particularly to FIG. 1, the heating element herein disclosed comprises a sheath formed of a suitable impervious mineral material which is resistant to acids and the like. As presently preferred, the sheath is formed of a molded, impervious graphite such, for example, as that manufactured by Union Carbide Corporation under the mark Karbate. The lower end of the sheath (referring to the disposition of parts shown in FIG. 1) is internally threaded to receive a closure plug 11 which is also preferably formed of impervious graphite.

An electric heater 12, of any suitable construction, is disposed lengthwise in the lower end of the sheath, and a groove 14 is formed in the'outer wall of the sheath to indicate the upper limit of the heated length of the sheath. Preferably, an asbestos pad 111, with no cotton fibers, is disposed between the plug 11 and the lower end of the heater 12.

The upper end of the sheath 10 is externally threaded to receive an internally threaded coupling 15 which is also formed of acid-resistant material and presently is formed of molded polypropylene. A loose ring 16, also formed of polypropylene, is disposed between the lower end of the coupling 15 and a metal plate 17 having an opening 18 to loosely pass the sheath 10. The plate 17 may be secured to a suitable support so that the sheath may hang in a tank (not shown) which contains the solution to be heated. The upper end of the coupling 15 is closed by a polypropylene disc 19 which is sealed in position by a polypropylene cement.

The side wall of the coupling is formed with a threaded opening to receive a polypropylene conduit 20, and the threaded joint is sealed with polypropylene cement. The end of a vinyl tube 21 is stretched over the outer end of the conduit 20 and is also preferably sealed thereto. The tube 21 is of a length to extend to a junction box (not shown) and protects the lead wires disposed therein from acid fumes.

As shown in FIG. 1, a pair of insulated lead wires 22, 23 extend through the vinyl tube 21, the conduit 20, the coupling 15, the sheath l0, and are sealed to terminals of the electric heater 12. Granular refractory material 24, such as magnesium oxide, fills the interior of the sheath and is disposed in the space between the exterior of the heater l2 and the inner wall of the sheath. The sheath is subjected to a vibrating action at the time the refractory material is introduced into the sheath to insure that all space is filled. However, the refractory material is preferably not highly compacted because the sheath is relatively fragile and because the refractory material is required to provide for a reasonable amount of expansion when the heater is energized.

.At the time the sheath 10 is being filled with refractory material 24, a stainless steel tube 25 is supported within the upper open end of the sheath so as to be disposed at least in part within the refractory material. The lower end of the sheath is covered by a jacket 26 (see FIG. 4) of woven polypropylene cloth which is wrapped around the tube lower end and held in place by a wire 27 which is wound therearound and has its ends twisted together. The jacket prevents the refractory material from flowing through the tube 25 in the event the heater is inverted during shipping or handling.

Before the coupling 15 is threaded onto the upper end of the sheath and sealed thereto, as by polypropylene cement, a flat spring plate 28, of a length slightly greater than the inside diameter of the sheath, is positioned inwardly of the upper end of the latter. The plate 28 constitutes a grounding element and has a terminal clip 29 spot welded thereto, as best shown in FIG. 5. A lead 30 extends from the plate through the coupling 15, the conduit 20 and tube 21 and it has its extremity suitably grounded. The plate is initially fiat, but as it is forced into the sheath, it is slightly bowed, as seen in FIG. 1, and its corners dig into the wall of the sheath not only for good electrical contact but also to hold the plate in position.

Thereafter, a suitable cement 30 is poured into the upper open end of the sheath to seal the upper surface of the refrac' tory material and to encapsulate the grounding plate 28 as well as to seal around the adjoining portions of the leads 22, 23 and 30. The cement is preferably an epoxy which will air harden, such as Tecoset.

The heater thus formed is suitable for heating highly corrosive substances, such as acid, since the impervious graphite sheath will resist deleterious attacks by acid, and the remaining parts resist corrosive action of the acid fumes. The support plate 17 may be coated with rubber or the like, so it too will resist corrosive attack. During operation, the heating element 12 may expand since the relatively loosely packed refractory material will permit this. Also, the sheath 10 may breathe, that is, air may enter or exit during off and on cycles, through the stainless steel tube 25. The grounding plate 28 provides safety in the event a crack appears in the sheath and solution enters to short circuit the heating element, and thus guards against the danger of having the solution and the tank become a conductor for electrical currents from the shorted heating element.

I claim:

1. A heater for heating highly corrosive solutions contained within a tank, comprising a sheath formed of an impervious mineral material which resists the corrosive action of said solutions, said sheath having an end adapted to be disposed within the solution to be heated, an electric heating element within said sheath, a coupling member formed of material which will resist the corrosive action of said solution or the fumes therefrom, said coupling member being joined to the opposite end of said sheath in sealed manner, conductor leads extending from said heating element through said sheath and coupling member and adapted to be connected to a source of electrical energy, means sealing said opposite sheath end, and a tube extending through said sealing means and having one open end within said sheath and the opposite open end within said coupling member to permit air to flow between the interior of said coupling member and the interior of said sheath.

2. The construction of claim 1 wherein said sheath is formed of impervious graphite.

3. The construction of claim 1 wherein said sheath contains granular refractory material below said sealing means and said one tube end is covered with pervious means which prevents refractory material from entering said tube.

4. The construction of claim 3 wherein said sheath is filled with granular refractory material to a point short of said opand outwardly of said sheath for connection to a source of electrical energy, and a grounding element comprising a metallic member spanning the opening in said sheath with ends thereof in electrical engagement with opposed portions of the inner wall of said sheath, and aconductor lead electrically connected to said metallic member and extending outwardly of said sheath for connection to a ground.

6. The construction of claim 5 wherein said sheath is formed of impervious graphite.

7. The construction of claim 6 wherein said grounding element is a plate of spring metal which is bowed upon insertion within said sheath so that marginal portions thereof are springpressed against the wall surface of said sheath.

8. A heater for heating highly corrosive solutions contained within a tank, comprising a sheath formed of impervious graphite, said sheath having one end adapted to be disposed within the solution to be heated, an electric heating element within said sheath and extending from said one sheath end to a point short of the other sheath end, conductor leads extending from said heating element and outwardly of said sheath for connection to a-source of electrical energy, granular refractory material filling the space within said sheath and surrounding said heating element, said refractory material stopping short of said sheath other end to leave a space, a grounding element comprising a plate of spring metal which is bowed upon insertion within said space so that marginal portions thereof are spring-pressed against the wall surface of said sheath surrounding said space, a conductor lead electrically engaged with said plate and extending outwardly of said sheath for connection to a ground, an epoxy cement seal transversely filling said space and overlying said refractory material and encapsulating said plate and sealing around the leads for said heating element and said grounding plate, and a tube extending through said cement in sealed manner and having one end opening on the side of said cement which faces said refractory material and the opposite end opening on the other side of said cement.

9. The construction of claim 8 wherein said sheath is formed with a groove in its outer surface to indicate the extent of the heated length of said sheath.

10. A heater for heating highly corrosive solutions contained within a tank, comprising a sheath formed of an impervious mineral material which resists the corrosive action of said solutions, said sheath having an end adapted to be disposed within the solution to be heated, an electric heating element within said sheath, a coupling member formed of material which will resist the corrosive action of said solution. or the fumes therefrom, said coupling member being joined to the opposite end of said sheath in sealed manner, conductor leads extending from said heating element through said sheath and coupling member and adapted to be connected to a source of electrical energy, and a hardened cement within said opposite sheath end to close the same except for an opening through the cement to permit air to flow between the interior of said coupling member and the interior of said sheath. 

1. A heater for heating highly corrosive solutions contained within a tank, comprising a sheath formed of an impervious Mineral material which resists the corrosive action of said solutions, said sheath having an end adapted to be disposed within the solution to be heated, an electric heating element within said sheath, a coupling member formed of material which will resist the corrosive action of said solution or the fumes therefrom, said coupling member being joined to the opposite end of said sheath in sealed manner, conductor leads extending from said heating element through said sheath and coupling member and adapted to be connected to a source of electrical energy, means sealing said opposite sheath end, and a tube extending through said sealing means and having one open end within said sheath and the opposite open end within said coupling member to permit air to flow between the interior of said coupling member and the interior of said sheath.
 2. The construction of claim 1 wherein said sheath is formed of impervious graphite.
 3. The construction of claim 1 wherein said sheath contains granular refractory material below said sealing means and said one tube end is covered with pervious means which prevents refractory material from entering said tube.
 4. The construction of claim 3 wherein said sheath is filled with granular refractory material to a point short of said opposite sheath end to leave a space thereat, and wherein epoxy cement is disposed within said space to seal said sheath opposite end, and wherein said tube extends through said cement.
 5. A heater for heating highly corrosive solutions contained within a tank, comprising a sheath formed of impervious material which resists the corrosive action of said solutions, said sheath having one end adapted to be disposed within the solution to be heated, an electric heating element within said sheath, conductor leads extending from said heating element and outwardly of said sheath for connection to a source of electrical energy, and a grounding element comprising a metallic member spanning the opening in said sheath with ends thereof in electrical engagement with opposed portions of the inner wall of said sheath, and a conductor lead electrically connected to said metallic member and extending outwardly of said sheath for connection to a ground.
 6. The construction of claim 5 wherein said sheath is formed of impervious graphite.
 7. The construction of claim 6 wherein said grounding element is a plate of spring metal which is bowed upon insertion within said sheath so that marginal portions thereof are spring-pressed against the wall surface of said sheath.
 8. A heater for heating highly corrosive solutions contained within a tank, comprising a sheath formed of impervious graphite, said sheath having one end adapted to be disposed within the solution to be heated, an electric heating element within said sheath and extending from said one sheath end to a point short of the other sheath end, conductor leads extending from said heating element and outwardly of said sheath for connection to a source of electrical energy, granular refractory material filling the space within said sheath and surrounding said heating element, said refractory material stopping short of said sheath other end to leave a space, a grounding element comprising a plate of spring metal which is bowed upon insertion within said space so that marginal portions thereof are spring-pressed against the wall surface of said sheath surrounding said space, a conductor lead electrically engaged with said plate and extending outwardly of said sheath for connection to a ground, an epoxy cement seal transversely filling said space and overlying said refractory material and encapsulating said plate and sealing around the leads for said heating element and said grounding plate, and a tube extending through said cement in sealed manner and having one end opening on the side of said cement which faces said refractory material and the opposite end opening on the other side of said cement.
 9. The construction of claim 8 wherein said sheath is formeD with a groove in its outer surface to indicate the extent of the heated length of said sheath.
 10. A heater for heating highly corrosive solutions contained within a tank, comprising a sheath formed of an impervious mineral material which resists the corrosive action of said solutions, said sheath having an end adapted to be disposed within the solution to be heated, an electric heating element within said sheath, a coupling member formed of material which will resist the corrosive action of said solution or the fumes therefrom, said coupling member being joined to the opposite end of said sheath in sealed manner, conductor leads extending from said heating element through said sheath and coupling member and adapted to be connected to a source of electrical energy, and a hardened cement within said opposite sheath end to close the same except for an opening through the cement to permit air to flow between the interior of said coupling member and the interior of said sheath. 